RDMA/siw: Remove set but not used variables 'rv'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/infiniband/sw/siw/siw_cm.c: In function siw_cep_set_inuse:
drivers/infiniband/sw/siw/siw_cm.c:223:6: warning: variable rv set but not used [-Wunused-but-set-variable]

Fixes: 6c52fdc2

 ("rdma/siw: connection management")
Link: https://lore.kernel.org/r/20190719012938.100628-1-maowenan@huawei.com
Signed-off-by: Mao Wenan <maowenan@huawei.com>
Reviewed-by: Bernard Metzler <bmt@zurich.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>